In the drilling of wells in formations beneath a body of water, it has become practice to employ, during drilling, a conduit which extends upwardly from the wellhead toward the vessel from which the drilling operation is being carried out, this conduit being of a diameter large enough to accommodate the drill string. Referred to as a riser, the conduit extends, under usual practices, for the entire distance from the wellhead to the vessel.
For a number of reasons, it is necessary to provide the riser with a predetermined buoyancy. Buoyancy is necessary to stabilize the riser, and to counteract the tendancy for the vessel and the riser to yield to lateral forces applied by currents and, at the vessel, by wind and waves. Best results have been achieved when buoyancy is distributed throughout at least a major portion of the length of the riser. A considerable amount of work and attention have been devoted by prior-art workers to the problem of providing underwater risers with buoyancy, and the state of the art is illustrated by the following U.S. Pat. Nos.
Re. 24,083, McNeil; PA1 1,712,803, Wood; PA1 1,746,132, Stokes; PA1 1,764,488, Zublin; PA1 2,187,871, Voorhees; PA1 2,476,309, Lang; PA1 3,017,934, Rhodes et al; PA1 3,221,817, DeVries et al; PA1 3,330,340, Hayes et al; PA1 3,354,951, Savage et al; PA1 3,359,741, Nelson; PA1 3,501,173, Petersen et al; PA1 3,605,413, Morgan; PA1 3,768,842, Ahlstone; PA1 3,858,401, Watkins;
Though some proposals of the prior-art have met with substantial success, there has been a continued need for improvement, particularly in view of the increasing underwater depths at which drilling is being carried out. One problem area is the need for surrounding the riser without having stresses set up in the riser pipe as a result of bending and elongation of the jacket structure. Another area of difficulty has been the problem of arriving at a structure in which buoyancy can be predetermined practically and with reasonable accuracy.